Waiver: intentional relinquishment of a right, requiring knowledge, voluntary abandonment, and reliance-based conduct. Waiver is the intentional relinquishment of a legal right, either express or implied from conduct, and may also arise by equitable or promissory estoppel where a representation was intended to be acted on and was relied upon. Recognition of waiver requires knowledge of the right, voluntary and intentional abandonment, and conduct relied upon by the other party that alters their position; mere indulgence or inaction is insufficient. Statutory rights can be waived by agreement or conduct, subject to public interest limitations, and the party pleading waiver bears the burden of proof.